The invention relates to a device for the connection of two tool portions, namely a tool head and a tool holder of machine tools, comprising a fitting pin provided on one tool portion and surrounded by an annular surface extending perpendicularly to the pin, a mating bore provided in the other tool portion for receiving the fitting pin and surrounded by an annular end face, a recess provided in the bore of the other tool portion, tension means arranged in the recess for a movement at least partly in radial direction, and abutment means provided at the pin cooperating with the tension means to convert a radial movement of the tension means into an axial movement of the pin to draw the annular surfaces of the tool portions tightly against each other upon operation of actuating means.
A device of this kind is known from UK-document 2 212 745. Two radially aligned internal threads are provided. Each one forms a recess. The tension means consist of screws threaded radially into the internal threads. The screws press radially against a radial bolt provided in a transverse bore of the pin. The ends of the bolt are wedge-shaped, to convert the radial movements of the screws into an axial displacement of the pin.
Another device for the connction of two tool portions as known from the EP 310 942 Al uses an axial drawbar urging tension balls radially outwards into recesses of the tool holder to couple a tool head.
Both known devices have the same disadvantage that the tension arrangement requires space in the interior of the pin of the one tool portion, wherefore axial connections extending through the coupling device--for instance coolant and hydraulic conduits, electric current wiring and mechanical rods and lever systems--cannot be installed. A further disadvantage consists in that the means for the conversion of radial forces into an axial tension stroke comprise only few small dimensioned wedge surface areas, which are subjected to high stress and because of abrasion the coupling device has a limited working life.